You really should not be spending your time thinking about what rules apply to more vs. greater--especially if you are all about efficient studying.
The GMAT does not test this.
Having said that, I can think of several examples that violate "rules" that were previously mentioned.
For example, using "greater than" for numbers..
What about this? : "His love for his country was greater than anything one could imagine."
Another one: use "more than" for objects
What about this? : "He studies more than any other GMAT student."
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Anyway, my point is not to think of rules.
Instead, think of "More than" as a general term and "greater than" as a specific example--like a subset of "more than"
Also, think of it in terms of nouns vs. verbs/adjectives.
With verbs, you cannot use "greater than"--
but for nouns, you can use either "greater than" or "more than"
"More persistence than a marathon runner" [noun] - OK
"Greater persistence than a marathon runner" [ noun] - OK
"Number of birds is greater than..." [noun] - OK
"Number of birds is more than..." [noun] - OK
"Runs more than a typical athlete" [verb] - OK
"Runs greater than a typical athlete" - [verb] WRONG
"He is more talented than his brother" [verb/adjective] - OK
"He is greater talented than his brother" - [verb/adjective] WRONG
"Gandhi is a greater man than..." [noun] -OK
"Gandhi is more of a man than..." [noun] - OK
Notice "greater than" is more limited than "more than."
Anyway, if you've read this far, you're spending too much time on the little things that DON'T MATTER. I advise you study efficiently so you don't waste your time.